1. Technical Field of the Invention
The present invention relates to an electromagnetically operating setting device for oscillatingly movable control elements on displacement engines, in particular for flat slide valves and lift valves, comprising a spring system and two electrically operating switching magnets, called working magnets in the following, by means of which an armature actuating the control element can be moved into two opposing switching positions, wherein the place of equilibrium position of the spring system lies between the two switching positions and the working stroke of the control element can be varied by changing the position of the pole surface of a working magnet and of the base of one or more springs of the spring system.
2. Discussion of the Related Art
In a setting device of the aforementioned kind, the control element of a displacement engine is held in the closed state by a compression spring. Another compression spring acts on the armature interacting with the control element so that the position of equilibrium of the spring system lies in the center or close to the center between the end positions of the movement of the armature. The end positions of the movement of the armature are at respective electrically actuated working magnets. To switch this device, one working magnet is excited and the other is switched off. Due to the force of the prestressed spring, the armature is accelerated upon release as far as the counteracting force of the other spring on its further path. Due to this friction, the armature cannot reach the opposing end position. The armature is attracted by the tractive force of the working magnet over the remaining distance.
In contrast to switching systems that attract the armature against the force of a spring over the entire stroke, with this system a significant reduction in the electric energy supplied and the size of the model is obtained. Owing to the small air gap to be bridged, the radial dimension of the winding window can be kept small. This is especially important with respect to the use of the setting device on displacement engines.
The working stroke of such a setting device is designed in such a manner that an opening has an adequate cross-section for the largest mass flow at the control element of a displacement engine and thus throttling is avoided.
With smaller mass flows, which occur when displacement engines, and especially internal combustion engines, are operating under partial load, operating the setting device at this maximum working stroke is inefficient since the electric energy to be supplied to change the position of the control element increases as a function of the stroke of the control element. Thus, a decreased stroke of the control element, in particular a decreased valve lift, is desired for energy reasons. Furthermore, a decrease in the cross-section of the opening results in an increase in the velocity of flow at the control element or at the control valve, a state that contributes to an improvement in the multi-phase fuel induction, especially in the air/fuel mixing in internal combustion engines.
Known systems to vary the working stroke of a setting device of the functional principle described above operate with switching or adjusting systems that are arranged outside the setting device or act together on several setting devices, as known, for example, from U.S. Pat. No. 4,777,915. A significant drawback of this design is a slow adjusting procedure which extends over several cycles of the internal combustion engine and renders digital control of the setting device difficult.
Accordingly, it is an object of the present invention to be able to fix in at least two different positions the working stroke of the setting device. This change-over is to take place in an internal combustion engine in a time span that is distinctly shorter than the time it takes for an internal combustion engine to go through one cycle.
Other objects and advantages are apparent from the specification and drawings which follow.